FIG. 1 illustrates a turbomachine 1 of the type with unducted propellers. It comprises from upstream to downstream, in the direction of airflow shown by arrows F, a compressor 2, an annular combustion chamber 3, a high pressure turbine 6, and two countrarotating low-pressure turbines 8. Each low-pressure turbine 8 is connected to an outer propeller 9, the two propellers being arranged coaxially behind the other about a longitudinal axis A of the turbomachine 1 and each comprising a plurality of blades P uniformly distributed about said axis.
For this purpose, each propeller is fixed on a ring 10 conventionally comprising (FIG. 2) an annular rotor body 11 generally polygonal (known as polygonal ring), centred on the longitudinal axis A of the turbomachine and having a series of radial cylindrical housings 12, distributed uniformly about the axis A, provided to receive the blades of the propeller. Each housing 12 further receives a crown on which the body of a plate adapted to receive the root 14 of a blade P is fixed. This crown is rotatably mounted in the housing 12 receiving it, which adjusts the angular orientation of the blade P.
In conventional terms, the annular bodies 11 are made of metallic materials such as titanium due to its low density and its good mechanical properties. In fact, the annular body 11 undergoes considerable tangential and axial forces under the effect of centrifugal loads due especially to its considerable diameter (around 1600 mm). It is therefore important that the annular body is capable of mechanically resisting the loads applied to it. However, current annular bodies 11 remain relatively heavy.
It has already been proposed to make the annular body 11 from composite material of the fibrous reinforcement type densified by a matrix. Reference could be made especially to document FR 2 992 677, in the name of the applicant, which describes the existence of such rings. It is true that these annular bodies exhibit a considerable gain in mass in comparison with conventional metallic bodies. But in practice the minimal continuity in fibres of the composite material in the annular body does not produce a propeller ring sufficiently mechanically resistant to support centrifugal loads when the turbomachine is operating.